Gas turbines are widely used in industrial and power generation operations. A typical gas turbine includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air enters the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through nozzles in the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
It is widely known that the thermodynamic efficiency of a gas turbine increases as the operating temperature, namely the combustion gas temperature, increases. However, if the fuel and air are not evenly mixed prior to combustion, localized hot spots may form in the combustor near the nozzle exits. The localized hot spots increase the chance for flame flash back and flame holding to occur which may damage the nozzles. Although flame flash back and flame holding may occur with any fuel, they occur more readily with high reactive fuels, such as hydrogen, that have a higher burning rate and wider flammability range. The localized hot spots may also increase the production of nitrous oxides in the fuel rich regions, while the fuel lean regions may increase the production of carbon monoxide and unburned hydrocarbons, all of which are undesirable exhaust emissions.
A variety of techniques exist to allow higher operating temperatures while minimizing localized hot spots and undesirable emissions. For example, various nozzles have been developed to more uniformly mix higher reactivity fuel with the working fluid prior to combustion. The higher burning rate of higher reactivity fuel, however, still creates an environment conducive to flame flash back and/or flame holding events. As a result, continued improvements in cooling provided to a combustor cap to cool the combustor cap, reduce undesirable emissions, and/or reduce the occurrence of flame holding or flash back would be useful.